How does an automotive service technician use specifications?

How does an automotive service technician use specifications?
Specifications covers a wide range of things, especially pertaining to mechanical objects, be they automobiles, heavy equipment, aircraft, etc. The specifications also define parameters by which equipment should be operating within. This can include measurements of physical dimension (for example, measuring out cylinders after an engine is disassembled to ensure they're within spec, or measuring brake components to ensure they're not excessively worn) or measurements of force, current, volume, etc. (for example, attaching a flow gauge to a hydraulic system to ensure the hydraulic pump is producing the right amount of flow).